I'm skeptical of this theory as well, but I'd point out that our observations show that at galaxy scales, gravity is much stronger in certain places than we'd predict using our current model of gravity and the matter we can otherwise detect, and at even larger scales the acceleration of the universe's expansion is being driven by something we don't understand.

Right now, the dominant theory in cosmology is that each of these observed phenomena are driven by dark matter and dark energy, but we don't have any direct evidence of the existence of either, just indirect evidence that stuff doesn't behave as we might expect.

So it's a choice between theories that don't make intuitive sense, and break some fundamental assumptions about physics.